Known in the art is a belt-type apparatus for producing high pressure, comprising a pair of punch assemblies the frustoconical end portions of which are enclosed by a metal belt member (cf., e.g., U.S. Pat. No. 3,075,245; Cl. 425-77, published January 29, 1963).
In the abovementioned apparatus the area between the punches and the belt is filled with a solid medium plastic under pressure, such as pyrophilite or catlinite (lithographic stone). The frustoconical ends of the punches in conjunction with the belt member define a high pressure vessel or chamber accommodating the solid medium, i.e. pyrophilite or catlinite, which surrounds a specimen material in said chamber acting to transmit pressure thereto. Oppositely directed ends of the punches face a press means. Under the action of the press means the punches are caused to move towards the center of the high pressure chamber to thereby compress the solid medium surrounding the specimen being tested and the medium disposed between the punches and the metal belt. A certain amount of the solid medium tends to flow into a gap between the punch assemblies and the belt member which affords the punches to be driven towards each other. The remainder of the solid medium is subjected to compression which causes a high pressure to arise therein. A certain distribution between a portion of the solid medium that flows out of the chamber and that which is subjected to compression enables the punches to be driven towards each other and obtain high pressure in the solid medium surrounding the specimen. As the punches are driven together, the gap between the punches and the belt member decreases which results in less solid medium to flow therethrough.
Finally, the punches terminate their reciprocal approach due to the fact that, regardless of a further possible increase in the force applied to the outer ends thereof, the gap between the punches and the belt assembly becomes so insignificant as to prevent the flow of the solid medium therethrough. The maximum pressure in the solid medium and, accordingly, the pressure obtainable in the specimen being tested is determined by the value of compression force exerted on the solid medium enclosing the specimen.
Therefore, the value of obtainable pressure depends on the gap between the punch assemblies and the belt member, which cannot be raised above 70 kilobars.
In addition, in the heretofore described apparatus for producing high pressure the frustoconical punches are subjected to considerable deformation along the longitudinal axis of symmetry thereof under the action of the pressure exerted thereupon by the solid medium surrounding the specimen being tested. Said deformation may result in damage of the punch working surfaces. Further, this deformation reduces the value of pressure obtainable in the solid medium. The reason for the deformation of the working surfaces of the punch assemblies is inherent in the construction thereof, wherein the area of the working surfaces of the punch assemblies which is acted upon by the high pressure produced in the high pressure chamber is several times smaller than that of the punch area (in some instances one tenth of the latter) to which the press effort is applied. As a result, in the punch portion adjoining the solid medium enclosing the test specimen normal axial stresses appear of the magnitude by far exceeding those acting upon the punch surface facing the press means and subjected to a uniformly distributed force from the press means.
In part, the axial deformation of the punch surfaces may be reduced through a constructional arrangement of the punches or dies according to another known apparatus for producing high pressure as exemplified by U.S. Pat. No. 3,854,854, Cl. 425-77, published Dec. 17, 1974.
This apparatus comprises a pair of identical coaxially arranged dies, each of the latter being made up of two portions one of which is a working body with an end thereof being in direct contact with a solid medium plastic under pressure arranged to surround a test sample and subjected to a pressure transmitted thereto by this medium, whereas the other is a base plate with an end thereof facing a common die driving means, the other end facing a second surface of the working body and spaced a certain distance therefrom. The space between the opposed ends of the working body and the base plate is filled with a solid medium plastic under pressure, whereas the surfaces of these ends have identical annular grooves the axes of which coincide with the longitudinal centerline of the die, the inner edges of the grooves encircling the central portions of the working body and the base plate ends, the grooves being at least partially filled with the solid medium plastic under pressure.
The central portion of the bearing face of the working body is acted upon by a force, the value of which is equal to or greater than the force acting upon the face of the working body adjoining the solid medium which surrounds the test sample. Normal stresses appearing in the working body along the longitudinal centerline of the die caused by a pressure developed inside the solid medium surrounding the test sample are compensated for by the normal stresses developed in the working body along the longitudinal centerline of the die under the action of the force applied to the central portion of the working body facing the base plate of the die. This substantially contributes to the reduction of deformation of the working body end adjoining the solid medium surrounding the test sample and affords to produce a much higher pressure in the solid medium surrounding the test sample. However, the aforedescribed constructional arrangement fails to provide an omnidirectional force to be exerted upon the working body which, in turn, does not allow to obtain pressures in excess of 150 kilobars.
Still another known apparatus for producing high pressure, a ball-type apparatus, comprises a multi-die system in the form of a solid body of regular geometry, such as a ball or a cylinder, separated by the planes passing through the symmetry axis thereof (cf., e.g., British Pat. No. 1,200,934; Cl. B Olj 3/00, published Aug. 5, 1970).
The abovementioned apparatus features dies which are truncated at the ends thereof facing a sample being tested defining thereby a high pressure chamber containing a solid medium plastic under pressure, such as pyrophilite or catlinite, arranged to enclose the test sample. The die ends opposite to the respective truncated ends face a common die actuating means, whereas a space between the side faces of the dies is partially filled with a solid medium plastic under pressure such as catlinite or pyrophilite.
Under the action of a force exerted upon the die ends facing the common die driving means (in this case a liquid, e.g. kerosene compressed by means of a compressor) the dies are caused to move towards the test sample and thereby act to exert pressure upon the solid medium enclosing the sample being tested and the solid medium contained in the gaps between the side faces of the dies. Part of the media is caused to flow into the gaps between the die side faces which enables the dies to progress towards the center of the high pressure chamber. The solid medium which tends to remain in the high pressure chamber is therefore subjected to compression which results in a pressure produced therein.
Finally, the dies terminate their reciprocal approach due to the fact that, regardless of a further possible increase in the force applied by the die driving means to the outer ends thereof, the gap between the adjoining side faces of the dies tends to become so insignificant as to prevent the flow of the solid medium therethrough. A maximum pressure obtainable in the solid medium and, accordingly, in the test sample is determined by the value of compression force exerted upon the solid medium enclosing the test sample. The surface area of the die end facing the die driving means is several times greater than that of the die end adjoining the solid medium enclosing the test sample. Accordingly, the value of compression forces acting upon the die ends are inversely proportionate to the surface area thereof.
In the absence of an omnidirectional and uniformly distributed compression force acting upon the die end adjoining the solid medium enclosing the test sample, high stresses tend to develop, which stresses impart considerable axial deformation to the die in the direction from the center of the high pressure chamber towards the outer end of the die. This presents a major problem in producing a higher pressure in the high pressure chamber.
In order to provide a more uniform stress distribution in the die portion adjoining the solid medium enclosing the test sample, the dies can be arranged according to the invention described hereinabove (i.e. U.S. Pat. No. 3,854,854; Cl. 425-77, published Dec. 17, 1974).
The combined features of the both inventions provide an apparatus for producing high pressure of the ball type with each die made up of two parts along the longitudinal centerline thereof and enable to obtain a very high pressure (e.g., in excess of 300 kilobars) in the solid medium surrounding a test sample. However, such an apparatus has a high pressure chamber of small volume.
The hereinbefore described apparatus for producing high pressure (i.e. U.S. Pat. No. 3,854,854; Cl. 425-77, published Dec. 17, 1974) comprises a multi-die system each die, as was already described hereinbefore, being made up of two parts arranged coaxially, one of the parts being a working body with a face end thereof directly contacting a solid medium plastic under pressure arranged to surround a test sample and subjected to a pressure transmitted thereto by this medium, the other being a base plate with an end thereof facing a common die driving means, another end facing a second surface of the working body and spaced a certain distance therefrom. The space between the opposed ends of the working body and the base plate is filled with a solid medium plastic under pressure, whereas the surfaces of these ends have identical annular grooves the axes of which coincide with the longitudinal centerline of the die, the inner edges of the grooves encircling the central portions of the working body and the base plate ends, the grooves being at least partially filled with the solid medium plastic under pressure.
The central portion of the bearing face of the working body is acted upon by a force, the value of which is equal to or greater than the force acting upon the face of the working body adjoining the solid medium which surrounds the test sample. Normal stresses appearing in the working body along the longitudinal centerline of the die caused by a pressure developed inside the solid medium surrounding the test sample are compensated for by the normal stresses developed in the working body along the longitudinal centerline of the die under the action of the force applied to the central portion of the working body facing the base plate of the die. This substantially contributes to the reduction of deformation of the working body end adjoining the solid medium surrounding the test sample and affords to produce a much higher pressure in the solid medium surrounding the test sample.
The die working body of the heretofore described high pressure producing apparatus fails to effectively utilize the force acting upon the central portion of the working body end facing the base plate and by far exceeding the force acting upon the working body end adjoining the solid medium surrounding the test sample.